Throughout northern Nigeria, Christian churches are ramping up security as a militant Islamist sect, Boko Haram, targets places of worship. At a church in the northern city of Kaduna, Christians are refusing to let the near-constant threat of attack keep them away from Sunday services.

The bellman's call to the faithful at this Assemblies of God church in the Kakuri area of Kaduna have been joined by another now-familiar Sunday morning sound.

Near-daily violence in northern Nigeria is increasingly targeting churches. Bombings and other attacks have killed dozens of Christians in recent months.

Inside this church, parishioners clench their eyes shut and lift their hands skyward as their lips move in prayer during the service. Three armed policemen sit outside, their guns propped in front of them as they keep watch.

The head minister, Reverend Emmanuel Daudu, says trust in God does not mean letting down your guard.

"We don't fear but we are security-conscious, because we don't have to be relaxing and our enemies to take us unawares," said Reverend Daudu. "We have to be alert always, because we don't know their plans against us or against the church."

All vehicles are checked for weapons and explosives before they enter the compound. A dozen volunteer security guards, led by chief security officer Aminu Timothy Babah, patrol the grounds.

"We are feeling that, let's try and do what we are able to do, to do the best we can, to make sure that the tension that is rising in the minds of people at least is being cooled down or being reduced," said Babah.

A car bomb that exploded in Kaduna on Easter Sunday killed 40 people and wounded others. Many suspect the intended target was a nearby church compound.

The militant Islamist group Boko Haram has repeatedly pledged to "purify" northern Nigeria of Christians.

Though the vast majority of Boko Haram's hundreds of victims were Muslims, the sect has targeted churches in particular for several attacks. The most recent, at a university in Kano, killed 15 people. Witnesses said gunmen threw explosives and then fired at those trying to flee.

There are fears that attacks against Christians in this already volatile region could aggravate tensions and even spark unrest or reprisal attacks against Muslims.

Just days after the Kano attack, the head of the Christian Association of Nigeria, Pastor Ayo Oritsejafor, said it is getting increasingly difficult to restrain what he said are millions of frustrated Nigerians.

"We have tried to talk to them, advise them and stop them from doing anything that will not help matters," said Pastor Oritsejafor. "We have tried to stop them from retaliating, and it has worked thus far. But what we are saying is we don't know if we can still hold them back if this kind of thing continues."

At the Assemblies of God Church in Kaduna, mother of two, Amako Laraba, says nothing can keep her from church.

"When you send your children to school, you are little bit afraid what might happen in the town, but in the church we are safe," said Laraba. "he Bible teach me that we should have faith in God. This is our town. This is our home. This is where we should worship so we feel very free."

The two-hour service is a cathartic experience. Joyous bursts of singing break up bouts of fiery preaching and concentrated prayer.